Measuring instrument.



E. H. BRISTOL.

MEASURING INSTRUMENT.

APPLICATION FILED JAN. 10, 1913.

1 ,2?2,3%4. Patented July 9, 1918..

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, E $5M W W -a-M'5 a%% E. H. BRISTOL MEASURING INSTRUMENT.

APPLICATION FILED JANJO, 1913.

1 ,272,34=4. Patented July 9, 1918.

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E. H. BRISTOL.

MEASURING INSTRUMENT.

APPLICATION FILED JAN. 10, 19x3.

1 ,Q'YQ SQQ Patented July 9, 1918.

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EDGAR BRISTQL, OF FOXIBOBO, MASSACHUSETTS, ASSIGNOR TO THE FOXBOBU coreEANY, @F FOXBOBO, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

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Specification of Letters Patent.

Patented July 9., 191%.

Application filed. January 10, 1913. Serial No. 741,193.

and Commonwealth of Massachusetts, have invented an Improvement inMeasuring Instruments, of which the following description, in connectionwith the accompanying drawings, is a specification, like characters onthe drawings representing like parts.

This invention relates to instruments for indicating or recordingchanges in temperature pressure and the like.

As shown herein, the invention is embodied in a pressure responsiveinstrument for indicating and recording difie'rential pressures. p

The character of the invention may be best understood by reference tothe following illustrative embodiment description of an the accompanyingdrawthereof shown in ings, wherein:

Figure 1 is a front elevation of an illustrative gage embodying theinvention with a portion of the face of the gage broken away to disclosemechanism back of said face;

Fig. 2 is a side elevation of Fig.1;

Fig. 3 on an enlarged scale is a sectional detail of parts shown in Fig.1;

Fig. 4 is a section taken on line H of Fig. 3;

Fig. 5 on an enlarged scale is a view partly in vertical section andpartly in elevation of the apparatus mounted at the rear of the casingshown in Figs. 1 and 2;

Fig. 6 is a section taken on Fig. 5; and I Fig. 7 is a perspective vieWof a detail to be referred to.

Referring to the drawing, the illustrative instrument there shown asembodying the invention comprises a casing 1 (Fig. 1) in which is fixeda circularplate 3 adapted to receive and support a chart 4 graduatedradially to represent periods of time and circularly to represent anydesired units or scale of values, said chart being detachably secured toand rotated by a shaft 5 driven by a suitable clock mechanism (notshown) contained in the said .casing. An index or pointer shown hereinas. a pen index 7 is movable over said chart and may be caused line 6-6of to travel in a generally radial direction over said chart to indicateor record thereon a pressure prevailing at or during anyinstant orperiod of time.

To prevent the inadvertent marking of the chart by the index pen while.inserting or removing charts, there may be provided a device adjustableto support the index pen temporarily out of contact with the chart. Asshown herein, this device comprises an L shaped arm 7 (Figs. 1 and 7)fulcrumed on a bracket 7 which may be bifurcated for insertion beneaththe head of a usual screw 7 for securing the chart supporting platewithin the casing, When it is desired to insert or remove the chart thearm 7*- is rocked on its bracket sufficiently to engage and lift theindex pen out from contact with the chart. The pivotal connection of thearm with its bracket is sufficiently tight to cause the arm to remain inthis position. After the chart has been inserted the arm is rockeddownward again so that it lies between the index and the chart, butwithout engaging or in any way interfering with the operation of theindex.

To control the movement of the index there is provided a pressureresponsive expansion tube 9 (Figs. 5 and 6) composed of a series ofexpansible sections or dia'phragms adapted to be elongated or contractedby secured to a plate 11 (Fig. 2) on the rear of the casing 1 by abracket 13 (Fig. 5). Pressure is admitted to the interior of the tubethrough a pipe 15 connected to said bracket.

The tube 9 is mounted and inclosed within a chamber formed by a casing17 having a flange 19 detachably secured to said plate 11 by' suitablescrews. Pressure may be admitted to the interior of this chamber througha pipe 21. By the above described construction fluids of difierentpressures may be'admitted to the interior of said tube and chamberrespectively and the tube will expand or contract according to thepreponderance of the pressure within or withoutf the same.

To transmit .movements of the expansion.

tube to the index 7 referred to, an arm 23 (Fig. 5) may be secured tothe expansion the index 7 as more fully hereinafter 'de-- scribed. Oneleg of the yoke is entered through registeringholes in said arm' 27 andlink and the other leg of the yoke is entered through registering holesin said link and said arm 33. To vary the effective length of the arm 33it may be .provided with a series of holes, in any of'which the yoke maybe entered. The arms 25, 27, the link 29 and the yoke 31 may beconstructed as shown and claimed in my copending application, Serial No.704,953fi1ed June 21, 1912.

By inserting one leg of the yoke into the different holes of the arm 33a considerable journaled range of adjustment may be obtained, but toprovide a greater nicety of adjustment the arm 33 may have a flexibleyoke or U shaped portion 37 whereby the arm may be pulled from or pushedtoward the shaft 35 more or less and its efiective length varied asdesired. This flexible ortion, however, has sufficient inherentstidiless to hold the arm in the position to which it is adjusted.

The shaft 35 is j ournaled within a bearing tube 39 (Fig. 6) laterallyrecessed to receive and permit the connection of the arm 37 to saidshaft. The bearing tube 39 is threaded to the chamber base plate 11referred to and projects through and beyond the same a substantialdistance within the interior of the casing 1..

To transmit the rotative movement of the shaft 35 to the index 7 a shaft41 is provided secured to said index and having one end in an arm 43carried by posts 45 secured to the base plate 11 The pressure of the penof the index 7 on the chart will tend to shift the shaft 41 axially tothe left (Fig. 6). To oppose this movement there is provided on the arm43 an arm 47 having an offset end in which is threaded a stud 49carrying a jewel or other suitable end thrust resisting bearing 51engaged by the pointed end of the shaft 41.

The pressure of the index on the chart and the weight of the index tendalso to rock t e shaft 41 out of true alinement with the shaft 35. Itis, therefore, desirable to flexibly connect the shafts 35 and 41 sothat any departure thereof from true axial, alinement may not cause thesame te bind .tard its rotative movement.

any possibility of of the casing 1.

retarded by their bearings. The illustrative flexible connection shownherein is formed by extending an end of the shaft 35 slightly beyond thebearing tube 39 and introducing the same into a recess 53 in the end ofthe short shaft 41. To transmit rotative movement from the shaft 35 tothe shaft 41 a pair of resilient arms55 is provided forming part of theflexible connection, one of said arms being fast to the shaft 35 and theother fast to the shaft 41. As stated, the tendency of the index is tothrust the shaft 41 axially to the left (Fig. 6). The resiliency of thearms 55 is such that they tend to move to- Ward one another'and draw theshaft 35 axially so that its end seats in the recess 53 of shaft 41 andthus the shafts are properly coupled together. The pointof connection ofthe index with coupling point of the two shafts and the coupling pointis located but a short distance from the end of the long shaft bearing39. As a result, there is little liability of bending or straining thelongshaft in such a manner as to cause it to bind in its bearing and re-This is advant'ageous since any friction on said shaft will tend toprevent the accurate transmission of the movement of the tube to theindex.

One end of the bearing of the shaft 35 is in the casing 1..where thereis one pressure, and the other end is in the casing 17, where there maybe a different pressure. To maintain equal pressures on the ends of saidshaft and thereby prevent from this difierence in the bearing tube 39 isclosed from said (Fig. 6) having one bearing tube and axial thrustthereof pressure the end of Within the chamber 17 chamber by apipe57 endconnected to said the other endopen and communicating with the interiorof the cas-.

ing 1. j

The expansion tube is a sensitive piece of mechanism and it is importantto prevent injury thereto by compression or expansion thereef beyond itsnormal limits. While the difii erence between the pressures may becomparatively small, yet the pressures Within the tube and inthe casingindividually may be high. If a high pressure should be introduced in onebefore the other, it might either expand or contract the expansion tubeto such an extent as to strain the same beyond its elastic limitandthereby destroy the delicacy and accuracy thereof.

Clne of the objects of the invention is to provide means which will beeffective. for automatically equalizing the pressures within theexpansion tube and casing in the event that the pressure in eitherexceeds a predeterminedlimit- To this end there is interposed in thepipes 15 and 21 (Fig. 5) leading to the expansion tube and easingrespeetively, a pressure equalizing device comprising a casin 73- (Figs.2 and 5) divided y a partition 5 into two compartments 77 and 79. Thethrough the pipes 15 and 21 and through these respective compartmentswithout theiiuid in one compartment passing into the other compartment.

To permit the flow of fluid from either of the compartments to the otheron the occur rence of excessive pressures, suitable automatic valvemeans is provided for each compartment. As shown herein, this valvemeans includes expansion tubes 81 and 83, which may be similar in theirgeneral structure to the expansion tube 9 described.

One end of the expansion tube 81 is fixed to the partition 7 5. Toprovide communication from the interior of the expansion tube 81 to thecompartment 7 9 the fixed end of the tube is bored and communicates witha ll-shaped channel 85 in said partition 7 5 and leading to saidcompartment 79. The channel 85 is similar to the channel 87 shown inFig. 5.

One end or" the expansion tube 83 is also fixed to the partition 7 5. Toprovide communication between the interior of the expansion tube 83 andthe compartment 7 7 the fixed head of the expansion tube 83 is aperturedand communicates with a U-shaped channel 87 also in said partition 7 5and communicating with the chamber 7 7 The channels 85 and 87 aresimilar, but'in planes at right angles to one another.

The movable ends of the expansion tubes are provided with valve openingsfor cooperation with valve seats typified herein as the conical endsofscrews 89 threaded in bosses in the ends of the casing 7 3 andrendered tight by gaskets 91 in caps 93. These valve screws 89 may beadjusted to vary the tension and responsiveness of the expansion tubes81 and 83 as desired. To prevent tam poring with said valve screws afterthey are once set they may be inclosed in suitable housings 95.

When fluids are admitted through the chambers-77 and 7 9 at normalpressures the expansion tubes 81 and 83 will remain seated against thescrew valves 89, but if the pressure for example in chamber 77 exceeds aredetermined limit the expansion .tube 81 W ill be compressed and moveaway from the screw valve 89, thereby admittingthe fluid in thecompartment 77 into the interior of the expansion tube 81, thencethrough the chanincl 85 into the compartment 7 9. Similarly in case thepressure in the compartment 79 exceeds a predetermined limit theexpansion tube 83 will be compressed so as to move away from its screwvalve 89,.

thereby permitting the fluid in the compartment 79 to pass into theinterior of the expansion tube 83, and thence through the channel 87into the compartment 77.

fluid will normally flow Thus by thisvalve construction there isprovided means for-automatically equalizing the] pressures in thecompartments in case the pressure in either of them becomes excessiveand at the same time the equalizing effect will be transmitted throughthe pipes-15 and 21 to and into the index governing expansion tube andits chamber. As a result the pressures in said tube and chamber will beautomatically equalized and there will be no possibility of unduedistortion of the expansion tube.

By adjusting the valve screws 89 toward or from the expansion tubes 81and 83 the tension and responsiveness of the latter may be varied sothat they may be arranged to automatically open and permit theequalizing of the pressures at any desired pressure. For example, insome cases it is desirable to automatically equalize the pressuresbefore the index has traveled to the extreme high pressure limit of itsscale. By this adjustable valve construction the pressure equalizingpoint maybe set so that the pressure will be automatically equalizedwhen the index reaches the extreme high pressure limit of its scale orwhen said index is at any desired predetermined distance from the highpressure limit ct its scale.

Tn order to prevent corrosion or other injury from the liuids to thepressure responsive mechanism containedin the casing 17 the tube andcasing may be filled with oil or other suitable liquid. To this end oiltanlrs may be interposed in the pipes 15 and 21 for conducting thefluids to the receiver and easing. As shown herein two tanks 97 and 99are shown conveniently in one integral casing formed into two chambersby a dividing partition 101. This casing may be supported by the pipes15 and 21 or it may be attached to the rear of the casing 1 by screwsentered through ears 193 on said casing. Oil may be supplied to thetanks 97 and 99 through inlets normally closed by threaded plugs (Fig.6). The

oil transmits the pressure'of the fluids to the pressure responsivemechanism and at the same time separates the fluids from the mechanismand thereby insulates and protects the mechanism from any corrosive orother deleterious eli'ect from said fluids.

The volume of 'oil in the expansion tube volume and thereby raise thelevel in one of the oil tanks above the level in the other oil tank.This would create a difference in head in the two tanks which wouldcreate a ditlerential pressure which would affect the expansion andcontraction of the index com trolling tube 9. It is therefore veryimportant to provide equal volumes of oil Within and without theexpansion tube 9 in order that'there may be no difi'erence in the oillevels in the tanks which would affect the reading.

The space Within the tube containing casing 17 surrounding the tube isconsiderably greater than the space within the tube. The tank 97communicates with the tube 9 and the tank 99 communicates with thecasing 17. The tank 97 communicating with the smaller space is thereforemade sufliciently larger than the tank 99 communicating with the largerspace in order to compensate for the difference in the'volumes in thetube and casing.

The expansion and contraction of the index controlling tube 9 under theaction of different fluid pressures will cause the oil levels in thetanks97 and 99 to vary. For

example, if the tube 9 is expanded the oil level in the tank 97'feedingsaid tube'will tend to drop'and the oil level in the tank 99 feeding thetube casing will tend to rise. To compensate for this variation in oillevels and maintain the levels constantly equal in order that there maybe no modification of the indication from a difierence in oil headsthere is provided a mechanism which will now be described with moreparticular reference to Fig. 5.

As shown herein the illustrative mechanism for this purpose comprises anexpansion tube 97 substantially similar in 'construction andsize to theindex controlling expansion tube 9 described. This expansion tube islocated within the oil casing 97 and has one end mounted on a supportingframe 97 extending horizontally across said casing. To providecommunication between the tank 99 and the interior. of the expansiontube 97 the latter is. connected to said tank by a pipe 97. Itwill beapparent that the tube 97 being submerged beneath the level of the oilin the tank 97, if expanded, will cause the level of the oil to rise insaid tank and if, on the other hand the expansion tube 97 is contractedit will cause the oil level in said tank to drop. The expansion.

tube 97 a should expand andcontract in conformity with the expansion andcontraction of the index controlling tube 9 in order to cause the oillevel in the tank 97 to remain the same as the oil level in the tank 99.

Since the oil level in the tank 99 tends to rise while the oil level inthe tank 97 tends to fall the expansion of the submerged tube would notbe sufiicient to equalize the levels in the tanks were it not for thefact that said tube communicates with the tank 99 through the pipe 97and thereby withdraws oil from the tank 99 as said tube expands. K

To control the expansion and contraction of the submerged tube 97 inorder that it may be caused to expand and contract as the indexcontrolling expansion tube 9 expands and contracts there is provided acontrolling expansion tube 97 of the same general construction and sizeas the index controlling tube 9 and the submerged tube 97 a with thisdifference: that the controlling tube 1s of weaker metal, less stifl,and therefore more responsive to pressure than the tube 97*. Thecontrolling tube 97 is also located within the casing 97 and one endthereof may be conveniently secured to the top of said casing. Thecontrolling tube 97 communicates with the tank 99 through a pipe 97 Thecontrolling tube is connected to the submerged tube by a link or rod 97suitably connected to the opposed ends of the controlling and expansiontubes.

The operation of this level controlling device is as follows: If thefluid pressure in the pipe 15 and on the oil level in the tank 97 isgreater than the fluid pressure in the pipe 21 and on the oil level inthe tank 99 the index controlling tube will expand, and as a result, theoil level in the tank 97 tends to lower and the oil level in the tank 99tends to rise. The, pressure in the tank 97, being greater than that inthe tank 99,. will cause the controlling tube to collapse more or less.In doing so it will pull up the free head of thesubmerged tube 97 andcause the latter to expand, thereby causing the tube to have a greaterdisplacement and causing the oil level in the tank 97 to rise. Thesubmerged tube in expanding will draw oil from the tank 99 in proportionto its expansion. It would not be necessary to draw oil from the tank 99if the oil level therein I remained constant while the oil level in thetank 97 is lowering since then the increase in volume of the tube 97 awould cause a displacement of the oil suiiicient to compensate for thefall in level due to the expansion of the index controlling tube 9 andwould maintain the oil level in the tank 97 the same as the oil level inthe tank 99. But since the oil' level in the tank 99 is rising as theoil level in the tank 97 is lowering it is necessary to withdraw oilfrom the tank 99 to compensate for the tendency of the oil level to risein said tank. Thus by the device described the same oil-levels aremaintained in the tanks when the index controlling tube is expanding.

When the index controlling tube is contracting owing to a greaterpressure in the 97 to fall and said tube will force some of its liquidthrough the pipe 97 into the tank aaaaaaa sure of the oil within theindex controllingtube balances the pressure of the oil on the outside ofsaid tube.

The oil supply tanks, it will be observed, are located between theequalizing expansion tube valve mechanism and the index governing tube 9and its casing. As a result,

' the equalizing expansion tube valve mechanism is in a position toautomatically equalize the pressures on the surfaces of the oil in thetanks in the event that either of these pressures exceeds apredetermined limit.

T 0 control manually the admission of pressure to the; responsive tubeand its casing, suitable valve means may be interposed in the pipes 15and 21 preferably adjacent the casing 1. As shown herein this valvemeans (Figs. 1, 3 and 4) comprises a union 107 including ducts 109" and111 communieating with one of said pipes and duets 113 and 115communicating with the other pipe. To control the passage from the duct109 to the duct 111 there is provided a needle valve 117 threaded into abushing 119, the latter in. turn being threaded in a boss in said union.The needle valve 117 may be controlled by a knurled handle 121 and thebushing 119 may be set tightly against a packing 123 by a nut 125 onsaid bushing. The threads between the bushing and'boss and the threadsbetween the needle valve and bushing have the same pitch so that if theneedle valve handle 121 is held stationary the. bushing nut may be setup and adjusted against its packing Without disturbing the position. ofthe needle valve.

Admission from the duct 113 to the duct 115 is controlled by a needlevalve 127 similar to that already described.

To provide communication between the ducts 109, 111 and the ducts 113,115, a cross duct 129 is provided. To control the passage of fluidthrough this duct a needle valve 131 is provided similar to those justdescribed. The needle valve 131 is first opened and then the needlevalve 127. The opening of the latter valve will admit fluid into theduct 113 through the duct 129 to the ducts 111 and 115 simu taneously.As a result, equal pressures will be admitted within and without theexpansion tube. Next the needle valve 117 is opened admitting fluid.pressure through the duct 109 to the ducts 111 and 113. The pressureswithin and without the expansion tube will still remain equal. Then theneedle valve 131 is closed, thereby shutting off communication betweenthe ducts 109 and 111, and the ducts 113 and 115. As a result,communication between the pipes 15 and 21 will be closed and thepressures in the expansion tube and easing will be independent of oneanother.

Thus the valves may be progressively opened in such a manner as toprevent the admission of excess pressure within the expansion tube orcasing such as might compress or expand said tube beyond its normallimits.

This arrangement of controlling valve is not only desirable forregulating the initial introduction of pressure to the pressureresponsive mechanism, but also for adjusting the oil in the two tanks 97and 99 to the same level in filling said tanks.

To control the admission of pressures to the pipes leading into theautomatic valve equalizing mechanism, a union and needle valvecontrolling mechanism 132 (Fig. 2) similar to that just described inconnection with the union 107 may be provided in the portions of thepipes 15 and 21 leading to said automatic valve equalizing mechanism.

To permit the escape of air from the easing 17 in filling the same withoil, a needle valve 133 (Fig. 6) is set in said casing. This valve isopened while filling the casing but isclosed and remains closed afterthe casing has been filled.

1t Willbe observed that the needle valves in the union for controllingadmission to the expansion tube and its chamber are so arranged thatthey are capable of being operated to prevent excessive pressure on theintroduction of fluids to the expansion tube and chamber, but they mightnot be opened in proper sequence to prevent this excessive pressure. Itis therefore desirable to have an automatic valve arrangement. for theexpansion tube in order to prevent any possi bility of excess pressureon said tube from any erroneous operation of said valves. To this endthe movable end of the expansion tube is provided with a valve seat 135(Figs. 5 and 6) coiiperating with which is a valve 137 carried by an arm139 conveniently of wire and secured to the edge of said tube end as at141. To permit more or less lateral movement of the valve so that it mayreadily find its seat, the arm 139 may be provided with a U-shaped bend143. To cause the arm to tend to press the valve on its seat it may beof resilient material or may be provided with a coil spring portion 145.

To lift the valve .automatically from its seat when the tube 9contractsbeyond a predetermined limit, a stop 147 is provided herein inthe form of an offset bend of a wire 149 secured to a post 151 connectedto the casing base plate 11.

When the expansion tube contracts beyond a predetermined limit the valvearm 139 will engage the stop 147 and be automatically lifted from itsseat, thereby permitting the entrance of fluid from the easing into saidtube, thus automatically equalizing the pressures and preventing furthercontraction of the tube.

.To automatically open the valve on the expansion of the tube to apredetermined limit a stop 153 is provided, conveniently a continuationof the wire arm 149 forming the stop 147 referred to, and the valvecarrying arm, 1.3.9 is extended beyond the edge of .the expansion tubeand to present a reverse bend or heel 155.

When the tube expands to a predetermined limit the heel 155 will engagethe stop 153, and owing to the fact that the heel is be yond the pointofconnection of the arm with the tube, the arm will be rocked in such amanner as to lift the valve from its seat, thereby permitting theexcessive pressure within the indie to escape within the chamber andautomatically equalize the pres-- sures and prevent further expansion ofthe tube.

The automatic valve 137 has a further use. In filling the expansion tubewith oil the valve 137 will be automatically lifted from its seat andpermit the escape of air automatic expansion tube pressure equaliz ingdevice. The parts of the responsive mechanism are protected fromcorrosion or other deleterious eflect from the pressure fluids by theprovision for the filling of the expansion tube and the chambercontaining the same with oil. The flexible connection betwen the shaftsreduces their friction on their hearings to a minimum and enables theuse of a long shaftandbea'ring which will be efi'ective for resistingleakage from the expansion tube containing chamber. The oil in thecasing 17 surrounding the shaft 35 and its bearing continuouslymaintains said shaft properly oiled, which further insures ease ofrotation. The shaft arrangement as a whole is such that the turningthereof with the greatest possible ease is'assured.

Hence the shaft may be relied upon to transmit faithfully the movementsof'the expansion tube to the index.

Having described one illustrative embodiment of the invention, withoutlimiting the same thereto, what I claim as new and desire to secure byLetters Patent is:

Claims:

1. In an instrument of the class described, the combination of an index,an actuating .shaft therefor, responsive means, a shaft movable thereby,said shafts being substanaeraeee tially alined and a coupling for saidshafts having arms secured to said shafts and yieldable in the linethereof.

2. In an instrument of the class described, the combination of an index,an actuating shaft therefor, responsive means, a shaft movable thereby,said shafts being substantially alined and a coupling for said shaftscomprising a spring member transverse to said shafts and having armssecured thereto respectively.-

3. In an instrument of the class described, the combination of an index,an actuating shaft therefor, an end thrust bearing for said shaft,responsive means, a shaft movable thereby and substantially alined withsaid first shaft, and connecting means between said shafts includingyieldable means for pressing one axially toward the other.

4. In an instrument of the class described, the combination of an index,an actuating shaft therefor, an end thrust bearing for said shaft,responsive means, a shaft movable the'reby and substantially alined withsaid first shaft, and yieldable means for pressing it axially toward thesame comprising a spring'member having arms secured to the respectiveshafts.

5. In an instrument of the class described, the combination of indexmeans; responsive means to govern movement of said index means; andmeans connecting said index and responsive means including shafts, onehaving an end set in a recess in the other, and flexible means fortransmitting the rotation of one to the other.

6. In an instrument of the class described, the combination of indexmeans; a casing, responsive means therein to govern movement of saidindex means; and means for transmitting said movement from saidresponsive to said index means including a shaft projecting through saidcasing, a bearing for said shaft, and means for maintaining equalpressures in said bearing at the opposite ends of said shaftindependently of difierences in pressure within and without said casing.

7. In an instrument of the class described, the combination of'indexmeans; responsive means to govern movement of said index means; andmeans for transmitting said movement from said responsive to said indexmeans including a shaft, a bearing for said shaft, and means providingan equal pressure on the opposite ends of said bearing including a ductcommunicating with one end of said bearing. 7

8. In an instrument of the class described, the combination of indexmeans; responsive means to I govern said index .means; and means totransmit movement fromsaid responsive to said index means including ashaft, a bearing-.Ifor said shaft, and means for maintaining-equalpressures at the opnaraeee posite ends of said bearing irrespective ofthe pressure on said responsive means.

9. In an instrument of the class described, measuring means responsiveto difierential pressures, means forming passages for admitting thepressure fluid to the measuring means and bypass means between saidpassages, each including an expansion member in communication with onepassage and to bypass pressure sion tube valves opening to the other andmeans in said other passage cooperating with said member to provideavalve and valve-seat.

10. In an instrument of the class described, pressure measuring means,pressure conduits leading thereto and means sensitive to the pressuresinthe conduits reciprocally fluid from one conduit to the other on theoccurrence and during the continuance of determined pressure difierence.

11. In an instrument of the class described,the combination oi indexmeans; responsive means to govern movement of said index means; andmeans including expanfor automatically limiting the difference of thepressures acting on said responsive means.

12. In an instrument of the class scribed, the combination of. indexmeans; responsive means to govern movement of said index means; achamber for receiving, said responsive means; and means includingexpansion tube valve means having provision for automatically limitingthe difference of the pressures acting in said responsive means andchamber.

13. In an instrument of the class described,

the combination of index means; responsive means to govern movement ofsaid index means; and means for automatically limiting the difierence ofthe pressures within and Without said responsive means includingnormally closed expansion tube means and valve means'for automaticallypermitting the passage of fluid therethrough.

14:. In an instrument of the class described, the combination of indexmeans;

to govern movement of responsive means said index means; duct means foradmitting pressures to said responsive means; and

means for limiting the difi'erence of the ressures including chamberscommunicatmg with said duct means and expansion tube valve means forcontrolling the admission of pressure from one or said chambers toanother.

15. In an instrument of the class described, the combination of indexmeans; responsive means to govern movement of said indexmeans; a casingreceiving said responsive means; and means automatically to limit the-difi'erence of the pressures in said responsive means and casingincluding chambers communicating with said responsive means and easingrespectively, expandcating expansion tube means for si on tubes in saidchambers, and valve means coiiperating with said tubes.

16. In an instrument of the class described, the combination of indexmeans; responsive means to govern movement of said index means; a casingfor said responsive means; pressure conducting chambers communicatingwith said responsive means and casing respectively; and means forautomatically limiting the difference of the pressures between saidchambers including pressure responsive expansion'tubes in said chambers,a passage leading from the tube in one chamber to the opposite chamber,a passage leading from the tube in the latter chamber to the oppositechamber, and valve means for said tubes.

17. In an instrument of the class dcscribed,'the combination of indexmeans; responsive means to govern movement 0 said index means; a casingfor said responsive means; pipes for conducting fluids to.

bers communicating with said pipes for sup-- to said pressure responsiveand automatically operequalizing the levels of the liquid in saidchambers.

18. In an instrument of the class described, the combination of indexmeans; responsive means to govern movement of said index means; a casingfor said responsive means; means for preventing excessive pressure onsaid responsivemeans including a valve therefor and means forautomatically opening said valve respectively ou moveplying liquid meansand casing;

ments of said responsive means to predeter- I mined limits; tubes forconducting fluids to said responsive means and easing; valve means forcontrolling the passage of said fluids through said tubes; chain ersinterposed in said tubes respectively for supplying liquid to saidresponsive means and casing; and automatic expansion tube valve meansfor equhlizing the liquid levels in said chambers.

19. In an instrument or the class described, the combination of indexmeans; a

hollow diaphragm expansion tube to govern movement of said index means;and means for preventing excessive pressure on sai tube including avalve thereon and means for automatically opening said valve onmovements of said tube to predetermined limits.

20. In an instrument oi the class described, the combination of indexmeans; a hollow diaphragm expansion tube to govern movement of saidindex means; valve means on said tube; resilient means tendingto closesaid valve means; and means for automati- Cally openin said valve meanson movements of sai mined limits.

are

responsive means to .predeter- H1 21. In flan instrument of the classdehollow pressure responsive. expansion tube for governing said indexmeans; and means to prevent excessive pressures on said tube including avalve for said tube, means connecting "said valve to said tube, and stopmeans for engaging said-connecting means and automatically opening saidvalve on expansion or contraction of said tube to predeterminedliinits.

23. In an instrument of the class described, the combination of indexmeans; responsive .means for governing movement of said index means; achamber for said responsive means; means to introduce pres- I sures tosaid responsive means and chamher; and means automatically to equalizeexcessive pressures on said responsive means and in sa1d chamberincludlng a valvefor said responsive means and means for automaticallyopening the same on movements of said responsive means to predeterminedlimits.

24. In an instrument of the class described, the combination of indexmeans;

a responsive tube to govern movement of sa1d index means; a casing forsa1d tube; rece1ver's for supplying llquld to sa1d tube and casing; andmeans including expansion tube means for automatically maintainmg thesame liquid levels in said recelvers on the expansion and contraction ofsaid index overning tube.

25. In an instrument of the class described, the combination of indexmeans; a respbnsive tube for governing movement of said index means; acasing for said tube;

receivers for supplying liquid to said tube and casing; and meansincluding a sub- "merged expansion tubein one of said receivers forautomatically maintaining the same liquid levels in said receivers onthe expansion and contraction of said index governing means.

26. In an instrument of the ,elass ole-f scribed, the combination ofindex means; a responsive tube to govern movement of said index means; acasing containing said tube; receivers for supplying liquid to saidtube. and casing; and means including submerged and controllingexpansion tubes for auto matically maintaining the sanie liquid levelsin said receivers.

27. In an instrument of the class desive tube to lamest scribed, thecombination of index means; a responsive tube to govern movement of saidindex means; a casing for said tube; receivers for supplying liquid tosaid tube and casing; and means including a subindex means; a casing forsaid tube; re-

ceivers for supplying liquid-to said tube and casing; an expansion tubesubmerged beneath the liquid in one of said receivers; a controllingexpansion tube connected to said submerged tube; and means providingcommunication between said submerged and controlling tubes and the otherreceiver to control the liquid levels in said receivers.

29. In an instrument of the class described, the combination of indexmeans; a responsive tube to govern movement of said index means; acasing for said tube; re.- ceivers for supplying liquid to said tube andcasing; and means for controlling the liquid levels in said receiversincluding an expansion tube submerged in one of said receivers indexmeans; a casing' for said tube; re-

ceivers for supplying llquid to said tube and casing; and means forcontrolling the liquid levels in said receivers including submergedmeans having provision for providing varying displacement thereof. ,4

31. In an instrument of the class described, the combination of indexmeans; a respongovern movement of said index means; a casing for saidtube; receivers for supplying liquid to said tube and casing; and meansincludin submerged means and controlling means or the latter formaintaining the same liquid levels in said receivers on the expansionand contraction of said index governing tube.

32. In a device of the class described, the combination with pressuremeasuring means, ofa pressureequalizing device comprising, incombination, high and low pressure ducts leading to said measuringmeans; high and low pressure containing chambers communicatingtherewith; and means for-automatically tending to e ualize the pressuresin said chambers on t e attaining of a predetermined pressuredifi'erence in said ducts.

33. In a device of the class described, the combination with pressuremeasuring means of pressure receiving ducts leading to said measuringmeans; high andglow pressure chambers; means-providing communicationfrom said ducts to said chambers; and means tending to equalize thepressures having provision immediately responsive to a pressuredifference'in said ducts exceeding apredetermined amount.

34. In a device of the class described, the combination of an index;responsive means for controlling the same means for subjecting saidresponsive means to differential pressures; and means automaticallytending to equalize said pressures immediately on theirreaching apredetermined difference.

35. In an instrument of the class described, the combination of indexmeans; hollow responsive means to govern movement of said index means; achamber containing said responsive means; tubes leading to saidresponsive means and chamber; liquid receivers interposed in Said tubesand having provision for supplying liquid within and Without saidresponsive means; and means connecting said receivers whereby liquidfrom one chamber is automatically transferred to occupy space in theother to equalize the levels of liquid therein on changes of pressure.

-36. An instrument of the class described comprising responsive meansarranged for reaction to differential pressures; means to transmitpressures thereto comprising liquid columns; and means to by-pass liquldfrom one column to occupy space in the other on variations of pressureto equalize "the heads thereof.

37. An instrument of the class described comprising index means; anexpansion tube for moving the same; a casing inclosing said tube;connections comprising liquid containing chambers in communication withsaid tube and said casing respectively; and means to by-pass liquid fromone chamber to 0ccupy space in the other on-- variations of pressure tomaintain balanced the hydraulic pressures of the liquid on said tube.

38. An instrument of the class described comprising responsive meansarranged for reaction to differential pressures; means to transmitpressures thereto comprising liquid columns; and means renderedeffective by depression of the liquid level in one column by increase ofpressure thereon and actin temporarily to discharge suflicient liquifrom the other column so as to occupy space in the first named column tomaintain equality of the hydraulic pressures of said columns.

In testimony whereof, I have signed my name to this specification, inthe presence of two subscribing witnesses.

' EDGAR H. BRISTOL.

Witnesses:

HENRY T. WILLIAMS, JOHN R. Mou'rrrorr.

